Electronic part fabricated by intaglio printing

ABSTRACT

A pattern, in which a groove of an optional position is deeper than that of the other portion, is formed on a surface of a flexible resin sheet by laser process, and then a release layer is formed on the surface of the thus obtained pattern, thereby forming an intaglio plate. The intaglio plate is filled with Ag paste and then dried. The intaglio plate is then laminated onto an insulating substrate, on which a thermoplastic resin layer is formed using heat rollers. Thereafter, the intaglio plate is peeled from the insulating substrate so that the pattern of the Ag paste is transferred thereon, and the conductor pattern is formed through burning. Further, an insulating layer is formed so as to cover the conductor pattern and another conductor pattern is formed on the insulating layer, whereby forming a multilayered structure. In some cases, a difference in height of the lower layer conductor pattern is provided and the higher portion thereof functions as a via hole electrode for electrically connecting the lower and upper conductor patterns.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of application U.S. Ser. No.08/309,049, filed Sep. 20, 1994, now U.S. Pat. No. 5,609,704.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic part used for electronicapparatuses of various types and a method for fabricating the same, andmore particularly, to an electronic part fabricated by intaglio printingand a method of fabricating the same.

2. Description of the Related Art

In recent years, as electronic apparatuses become smaller, electronicparts used in the electronic apparatuses are more and more miniaturized.Under such conditions, conductor patterns are required to fulfill thefollowing requirements: to have a fine conductor line (hereinaftersimply referred to as line) constituting the conductor pattern; onincrease in thickness of a conductive film constituting the conductorpattern in order to lower line-resistance; and to have a multilayeredstructure in order to miniaturize the electronic parts.

Conventional conductor patterns of the electronic parts are fabricatedby printing a pattern of conductive paste such as a silver paste and acopper paste on an object (a substrate) employing printing techniquessuch as screen printing and intaglio printing, and then burning theprinted object. As an application of the intaglio printing, there is thefollowing printing method for forming a desired conductor pattern asdisclosed in Japanese Laid-Open Patent Publication No. 4-240792. Anintaglio plate corresponding to a conductor pattern to be formed isfilled with conductor paste (organic metal ink). After the conductivepaste is dried and cured, the pattern is transferred onto a substratewith a curable resin therebetween. As a result, a desired conductivepattern is formed.

In addition, for a hybrid IC circuit, a thermal head, or a transparentelectrode, a method utilizing thin film formation and etching may beused. This is because the width of each line and the interval betweenthe lines in the conductor pattern can be made finer by this method. Theprocess of the method is as follows. A thin film made of a conductivematerial such as gold, aluminum, ITO or the like is formed by vapordeposition or sputtering. A mask pattern corresponding to the desiredconductor pattern is formed by photolithography using a light-sensitiveresin. Then, the thin film made of the conductive material is etchedusing an etchant and the mask pattern. Lastly, the light-sensitive resinis removed, thereby forming the conductor pattern.

The above conventional methods, however, have the following problems.

Conventional screen printing can be carried out with equipment atrelatively low cost. Moreover, the number of steps required to form theconductor pattern are few. However, it is very difficult to form a fineconductor pattern so that the width of the line of the conductor patternto be formed is 70 μm or less by screen printing. Furthermore, it isalso difficult to reduce a line pitch to 150 μm or less. In addition,since the conductor pattern is uniformly formed by screen printing, itis impossible to make a difference in level (difference in height of theline) of the pattern according to design requirements.

It is possible to form such a fine conductor pattern so that the widthof the line is about 50 μm and the line pitch is about 100 μm byconventional intaglio printing. However, it is difficult to form aconductor pattern having a thickness of 5 μm or more. Therefore, anydecrease in the conductor resistance is limited to a certain extent.

On the other hand, making a fine conductor pattern in each layer issometimes insufficient for obtaining the electronic parts with thedesired high-density. Therefore, it is required to form a multilayeredstructure. Such a multilayered structure is formed by laminating severalsandwich structures respectively including a lower layer conductorpattern, an insulating layer and an upper layer conductor pattern. Inthis case, it is necessary to form via holes for connecting conductorpatterns of upper and lower layers to each other, which alsonecessitates making the via holes fine according to the fine conductorpatterns. However, in conventional printing methods including theaforementioned method in Japanese Laid-Open Patent Publication No.4-240792, it is very difficult to form the via holes having a diameterof 100 μm or less.

Moreover, it is required to form electrodes for connecting the upper andlower layers within the via holes in order to obtain a reliableelectrical connection between the conductor patterns of both layers.However, even if fine via holes having a diameter of 100 μm or less canbe formed, it is difficult to form the electrodes in the via hole ofsuch a small size by conventional methods.

In conventional intaglio printing, an intaglio plate made of rigidmaterial such as glass or silicon wafer is generally used. In such acase, during the step of transferring the conductor pattern onto theobject such as a ceramic substrate or a glass substrate with the curableresin therebetween, the intaglio plate is not sufficiently flexible whenthe intaglio plate and the object attached to each other are to beseparated. As a result, a strong peeling force is required to separatethem from each other off their surfaces.

In order to solve the above problems, a metal sheet having flexibilitymay be used as an intaglio plate. However, even in such a case, theshaping process (formation of a groove) of the intaglio plate isperformed by wet etching which is isotropic etching. Therefore, theshaping of an intaglio plate with a high aspect ratio, that is requiredto form such a conductor pattern that the conductor film is thick (inother words, the line in the pattern is high) with respect to the widthof the line, cannot be carried out.

On the other hand, as can often be seen in semiconductor techniques, theformation of the conductor pattern utilizing photolithography is usefulin forming the pattern of a small area with the width of line of severalμm or less. However, for forming the conductor pattern used in theelectronic parts, it is generally required to form a pattern of arelatively large area. In such a case, it is required to conduct aseries of steps including deposition of the conductive film, applicationof a resist, exposure, development, etching, and removal of the resistwith large equipment. Since such equipment is generally expensive, thecost for fabricating the conductor pattern is likely to increase.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method for fabricating anelectronic part including a first conductor pattern on a substrate byintaglio printing includes the steps of: (a) forming an intaglio plateby forming a groove on a surface of a flexible resin in a patterncorresponding to the first conductor pattern; (b) forming a releaselayer on the surface of the intaglio plate for facilitating theseparation of the intaglio plate and the substrate; (c) fillingconductive paste into the groove; (d) drying the conductive paste; (e)refilling the conductive paste so as to resoften the conductive pastedried in step (d) and compensate for the decrease in volume thereof andredrying the refilled conductive paste, the refilling and the redryingbeing repeated at predetermined times; (f) laminating the intaglio plateand the substrate at a temperature and pressure set in a predeterminedrange; (g) peeling the intaglio plate from the substrate so as tothereby transfer the pattern of the conductive paste onto the substrate;and (h) burning the transferred pattern of the conductive paste tothereby form the first conductor pattern.

According to another aspect of the invention, an electronic partincludes: a substrate; and a first conductor pattern transferred onto asurface of the substrate by intaglio printing using an intaglio plate,the intaglio plate being formed with a flexible resin by a laserprocessing.

Thus, the invention described herein makes possible advantages of (1)providing a method for fabricating an electronic part capable of forminga fine conductor pattern having a line of 10 μm or less in width and of5 μm or more in thickness and including a via hole electrode ofapproximately the same size as the line width at low cost with highreliability, (2) providing a method for fabricating an electronic partcapable of making a difference in level in the conductor pattern bymaking the thickness at a desired portion different from that of theother portions according to design requirements, (3) providing a methodfor fabricating an electronic part allowing the conductor pattern asdescribed above to be multilayered, and (4) providing an electronic partfabricated by the methods as described above.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view schematically showing a chip inductor fabricatedin accordance with one example of the present invention.

FIG. 1B is a cross-sectional view of the chip inductor taken along aline 1B-1B′ of FIG. 1A.

FIG. 2 is a flow chart showing the steps of a method for fabricatingelectronic parts in the example of the present invention.

FIG. 3 is a schematic view showing a fabricating step of an intaglioplate in the example of the present invention.

FIG. 4 is a cross-sectional view schematically showing the shape ofgrooves formed on a surface of the intaglio plate in the example of thepresent invention.

FIG. 5 is a schematic view showing a filling step of conductor pasteinto the intaglio plate in the example of the present invention.

FIG. 6 is a schematic view showing a laminating step in the example ofthe present invention.

FIG. 7A is a cross-sectional view schematically showing a laminatedstate of a polyimide intaglio plate and an insulating substrate in theexample of the present invention.

FIG. 7B is a cross-sectional view schematically showing a laminatedstate of a conventional glass intaglio plate and an insulatingsubstrate.

FIG. 8 is a schematic view showing a peeling step in an example of thepresent invention.

FIG. 9 is a graph showing burning temperature conditions in a burningstep in the example of the present invention.

FIG. 10 is a cross-sectional view schematically showing a shape of a viahole formed in the example of the present invention.

FIG. 11A is a plan view schematically showing a hybrid IC substratefabricated in accordance with another example of the present invention.

FIG. 11B is a cross-sectional view of the hybrid IC taken along a line11B-11B′ of FIG. 11A.

FIG. 12 is a cross-sectional view schematically showing another hybridIC substrate fabricated in the present invention.

FIG. 13 is a cross-sectional view schematically showing still anotherhybrid IC substrate fabricated in the present invention.

FIG. 14 is a cross-sectional view schematically showing still anotherhybrid IC substrate fabricated in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, examples of the present invention will be described by wayof illustrative examples with reference to the accompanying drawings.

EXAMPLE 1

Hereinafter, a first example of a method for fabricating electronicparts is described with reference to FIGS. 1 to 10, taking a method forfabricating a chip inductor 1 for high-frequency as an example. In thefigures, like components are indicated by the same reference numerals.

FIG. 1A shows a plan view of the chip inductor 1 of Example 1, and FIG.1B shows a cross-sectional view of the chip inductor 1 taken along asection line 1B-1B′.

The chip inductor 1 has an insulating substrate 2 having dimensions of2×1.25 mm, a spiral coil conductor (line) 3 formed on the surface of themiddle portion of the insulating substrate 2, and terminal electrodes 4a and 4 b formed on the both end portions of the insulating substrate 2.An outer end 3 a of the coil conductor 3 is connected to one terminalelectrode 4 a. An inner end 3 b of the coil conductor 3 is connected tothe other terminal electrode 4 b through a lead electrode 6 and a viahole electrode 7. The lead electrode 6 is provided on the uppermostsurface of an insulating layer 5 which is formed on the surface of theinsulating substrate 1 so as to cover the coil conductor 3. The via holeelectrode 7 connects the lead electrode 6 on the uppermost surface ofthe insulating layer 5 to the coil conductor 3 on the lowermost surfaceof the insulating layer 5.

The chip inductor 1 is fabricated by intaglio printing. Hereinafter, themethod for fabricating the chip inductor 1 is described in due order.Steps 210 to 310 in the following description are shown in the blockdiagram of FIG. 2.

First, referring to FIG. 3, Step 210 for forming an intaglio plate 20used in the process is described. The intaglio plate 20 is formed on aflexible polyimide film 15 having a thickness of 125 μm and fixed on anXY stage 16. A laser beam, having a wavelength of 248 nm of the UVregion, emitted from an excimer laser apparatus 11 is incident on a mask12 having a mask pattern corresponding to the spiral pattern of the coiland the pattern of the terminal electrodes to be thus formed. Passingthrough the mask 12, the laser beam is reflected by a mirror 13. Then,after being reduced in size through an imaging lens 14, the laser beamis incident on the polyimide film 15. The portion of the polyimide film15 illuminated by the laser beam is resolved by a photochemical reactionso as to form a groove 21 (see FIG. 4) corresponding to the lines of theconductor pattern. With the above process, the intaglio plate 20corresponding to a desired pattern is formed. About 4000 intaglio plates20 having dimensions of 2×1.25 mm are typically formed on the polyimidefilm 15 having dimensions of 100 mm×100 mm by repeating the aboveincident operation while moving the XY stage 16.

A process using a carbon dioxide gas laser or a YAG laser is the thermalresolution process using a laser beam of the infrared wavelength region.On the other hand, the process using the excimer laser is a photoresolution process using a laser beam of the UV wavelength region havinga peak power reaching several tens of MW. Moreover, since the pulselength of the laser beam is short, the thermal influence on the regionsurrounding the processed region is small. As a result, by the processusing the excimer laser, a minute process so as to form the patternhaving a line of 10 μm or less in width can be realized.

The portion of the surface of the polyimide film 15, on which the laserbeam is incident, is in a chemically highly activated state sincemolecular bonds constituting the polyimide film 15 are broken.Therefore, a chemical bonding is likely to occur in the region on whichthe laser beam is incident. This aspect is advantageous for forming therelease layer described later.

FIG. 4 shows a typical cross-sectional shape of the groove 21 of theintaglio plate 20 formed by the above method. The groove 21 can beformed so as to have a trapezoidal cross-sectional shape having a sideface with a tapered angle in the range of 2° to 60° by appropriatelyadjusting the characteristics of an optical system used in the laserprocessing step such as the focal depth of the lens. Owing to this, itis possible to easily transfer conductive paste filling the groove 21 onthe object in the succeeding process. The laser beam typically has arectangular shape of 8×24 mm in size when it is emitted from the laserapparatus 11, and a rectangular shape of 3.2×9.6 mm in size when it isincident on the polyimide film 15.

By providing an appropriate protecting layer on a surface of thepolyimide film 15 to be processed into the intaglio plate 20, it ispossible to protect a processed surface of the intaglio plate 20 frominteraction with plasma generated while the groove 21 is being formed.With this protecting layer, it is possible to prevent openings of thegroove 21 on the surface of the intaglio plate 20 from being deformed.As a material for the above-described protecting layer, for example,polyethylene terephthalate (PET), polycarbonate (PC) and polysulfone(PSF) may be used.

Next, the mask 12 is substituted by another mask for forming a via holeelectrode 7. Then, the laser beam is incident on a predeterminedposition of the groove 21 of the conductor pattern formed in theprevious process so as to form a cylindrical pit 22 (see FIG. 5)corresponding to the via hole electrode 7. In the formation of the pit22, it is also possible to carry out a fine process as in the formationof the groove 21. In addition, it is possible to form the pit 22 so asto have a tapered shape in order to facilitate the transfer of theconductor paste filling the pit 22. Alternatively, the pit 22 may have adifferent shape other than the cylindrical one.

With the method described above, the intaglio plate 20, whichcorresponds to the conductor pattern to be formed is formed, includingthe groove 21 having a depth of 20 μm corresponding to the line of 10 to50 μm in width and the pit 22 having a diameter of 60 μm correspondingto the via hole electrode having a diameter of 45 μm. The depths of thegroove 21 and the pit 22 can be arbitrarily changed by 0.2 μm as a unitand set at the most appropriate values by only changing the incidenttime period of the laser beam without affecting the width of the line(the width of the groove 21). The width of the groove 21 and thediameter of the pit 22 can be easily adjusted by modifying the size ofthe mask. Thus, according to the present invention, it is possible toreduce the line width of the conductor pattern to 10 μm or less or thesize of the via hole so as to match with such a fine line.

By using the polyimide film 15 as a material of the intaglio plate 20,as described above, it becomes possible for the intaglio plate 20 tohave flexibility. The effect obtained by this will be described later.

With the thus formed intaglio plate 20, the conductor pattern istransferred onto the surface of the object (the substrate). However, thepolyimide film 15 which is used as a material of the intaglio plate 20has insufficient release characteristics against the conductive paste,which is filled in the groove 21 and the pit 22 and then transferred.For this reason, the conductive paste tends to remain in the groove 21and the pit 22 in the transferring step. Especially, in the pit 22corresponding to the via hole electrode 7, the remaining conductivepaste is most likely to be found since the pit 22 is deep. This resultsin insufficient transfer. Therefore, in order to realize a substantiallycomplete transfer from the intaglio plate 20 to the substrate, Step 220of forming a release layer on the surface of the intaglio plate 20,especially on the surface of the groove 21 and the pit 22, is required.

In order to solve the above problems, the inventors closely examined therelease layer treatment on the polyimide film 15, especially from theview-points of the peeling force for the conductive paste and the lifeof the release layer. As a result, it is confirmed that to form therelease layer made of fluorine-carbon type monomolecular film by thefollowing method is most effective.

First, oxygen plasma is incident on the surface of the intaglio plate 20by an O₂ asher, there-by increasing the density of oxygen included inthe surface of the intaglio plate 20. On the other hand, a certainsolution is prepared, in which a non-aqueous solvent mixed with asubstance including fluorine-carbon groups and chlorosilane groups, forexample, CF₃(CF₂)₇(CH₂)₂SiCl₃, is dissolved at the concentration ofabout 1% in a mixed solution of n-hexadecane (alternatively, toluene,xylene, or dichlorohexyl may be used) 80%, carbon tetrachloride 10% andchloroform 8%. The intaglio plate 20 treated with oxygen as describedabove is dipped into the resultant solution so as to form an oxide filmon the surface thereof. A large number of hydroxyl groups are includedin the surface of the thus formed oxide film and therefore react withSiCl groups of the substance including fluorine-carbon groups andchlorosilane groups to cause a dechlorination reaction. As a result, afluorine-carbon monomolecular film, which is chemically absorbed by acovalent bonding, is formed on the entire surface of the intaglio plate20. The monomolecular film effectively functions as a release layer 23(see FIG. 5).

The portions requiring the strong peeling force in the peeling step aremainly the groove 21 and the pit 22, and therefore, it is desirable toform the release layer 23 on these portions. On the other hand, asdescribed above, the portion of the polyimide film 15 constituting theintaglio plate 20 in which the groove 21 and the pit 22 are formed bythe process using the excimer laser is in a chemically activated state.Therefore, the release layer 23 made of a fluorine-carbon monomolecularfilm described above is more bonded to the inside of the groove 21 andthe pit 22 requiring the large peeling force during the peeling step.Moreover, since the release layer 23 and the intaglio plate 20, i.e.,the above monomolecular film and the polyimide film 15 are bondedthrough a covalent bonding, their bonding is extremely strong, whichleads to the durability of the release effect. Furthermore, since thethickness of the release layer 23 is a small value, such as in the rangeof 100 to 1000 angstroms, the accuracy of the form of the intaglio plate20 is not affected and therefore it is possible to fill the intaglioplate 20 with a large amount of conductive paste.

As described above, the release layer 23 formed on the surface of theintaglio plate 20 in Step 220 has excellent characteristics.

Next, as Step 230, Ag paste 24 as the conductive paste is applied on thesurface of the intaglio plate 20, on which the release layer 23 isformed. Then, the applied surface of the intaglio plate 20 is scratchedby a squeegee 25, thereby removing the extra Ag paste 24 on the surfaceof the intaglio plate 20 as well as thoroughly filling the groove 21 andthe pit 22 with the Ag paste 24 (See FIG. 5).

According to the inventors' study on the material of the squeegee 25, itis preferred to use the squeegee 25 made of ceramic. Because a squeegeemade of resin or steel is likely to be damaged by extraneous substancesincluded in the Ag paste 24 and/or dust existing on the surface of theintaglio plate 20. Therefore, the surface of the intaglio plate 20 inturn is likely to be damaged by the flaws of the surface of a resin orsteal squeegee, resulting in a short life span of the intaglio plate 20.On the other hand, since the ceramic squeegee 25 is rigid, the tipthereof is less damaged by the extraneous substance and/or dust.Furthermore, by smoothing the tip of the ceramic squeegee 25 with a fineabrasive of No. 2000 or more, it is possible to prevent the wastage dueto abrasion for a long time. Thus, the ceramic squeegee 25 hardly causesany damage on the surface of the intaglio plate 20.

Next, the intaglio plate 20 filled with the Ag paste 24 is dried using acirculating type hot air dryer, thereby evaporating the organic solventincluded in the Ag paste 24 (Step 240). By this step, it is possible toobtain a sharper Ag shape by more suitably fitting the Ag paste 24 tothe groove 21 and the pit 22 of the intaglio plate 20. The drying meansis not limited to the above method.

The relatively deep groove 21 and the pit 22 are formed on the surfaceof the intaglio plate 20 described in Example 1. Especially, the pit 22has a maximum depth of 60 μm. So, if the intaglio plate 20 is rapidlydried at a temperature of 100° C. or more in the drying step 240, pinholes having a diameter in the range of 5 to 40 μm are likely to beformed in the Ag paste 24 filled into the groove 21 and the pit 22. Insuch a fine conductor pattern that the width of a line is 50 μm or less,the pin holes cause a disconnection of the conductor pattern after theburning thereof and therefore inhibit the formation of a high qualityconductor pattern.

Thus, the present invention adopts the drying step 240 which consists oftwo stages: a first stage of predrying at a temperature of 100° C. orless for 5 minutes and a second stage of drying at a temperature of 150°C. for 5 minutes. This prevents the pin hole formation and thus it ispossible to form the conductor pattern without disconnection after theburning. Alternatively, it is possible to obtain the same advantage ofinhibiting the pin hole formation as described above by raising thetemperature from room temperature to 150° C. with a moderate increaserate of 15° C. /minute or less in place of the predrying.

After the Ag paste 24 filling the groove 21 and the pit 22 is dried orcured in the above Step 240, the flexibility of the Ag paste 24 islikely to be lost. As a result, cracking tends to occur in the Ag paste24 due to the stress generated during the pattern transfer in the casewhere the conductor pattern with a fine line width (for example, 100 μmor less) is transferred, causing the disconnection of the conductorpattern after the burning. In order to avoid such a disadvantage, aplasticizer as much as 0.1 to 10 wt % is added to the Ag paste 24. Withthe addition of the plasticizer, it is possible for the Ag paste 24 tohave the appropriate flexibility after drying and therefore to preventthe cracking in the transfer step. As a plasticizer, an ester phthalatetype plasticizer, for example, dimethyl phthalate, diethyl phthalate, ordioctyl phthalate, can be used.

After the above drying step 240, the volume of the Ag paste 24 fillingthe groove 21 and the pit 22 is reduced by the amount corresponding tothe evaporated organic solvent. In order to fill up the reduced amount,the filling step and the drying step of the Ag paste 24 is repeated oncemore. The Ag paste 24 previously cured by the evaporation of the organicsolvent in the previous drying Step 240 is re-softened by the refillingof the Ag paste 24. By the refilling step 250 and the redrying step 260,the Ag paste 24 filling the groove 21 and the pit 22 can be put in aneven better shape, and the thickness of the Ag paste 24 can be set atthe same value as the depth of the groove 21 and the pit 22 of theintaglio plate 20.

If the Ag paste 24 remains on the unpatterned portion of the intaglioplate 20, especially, on each portion between the grooves 21, it maycause short circuits between the lines of the conductor pattern. Sincethe Ag paste 24 has viscosity and therefore tends to rope, the ropingphenomenon occurs during the scratching operation by the squeegee 25. Asa result, the Ag paste 24 remains on the portion where the Ag paste 24should be removed. However, when the refilling is carried out in thestate where the dried Ag paste 24 exists in the groove 21 and the pit22, the solvent of the Ag paste 24 newly applied to the unpatternedportion is absorbed by the dried Ag paste in the groove 21 and the pit22, thereby increasing the viscosity of the Ag paste 24 remaining on theunpatterned portion. As a result, the roping phenomenon does not occurwhen the Ag paste 24 on the unpatterned portion is removed by thesqueegee 25. Therefore, the Ag paste 24 remaining on the unpatternedportion can be removed with ease. Accordingly, the conductor pattern, inwhich the short circuit between the lines does not occur, can be formed.

In the description of Example 1, the refilling step 250 and the redryingstep 260 are repeated once, respectively. However, Steps 250 and 260 maybe repeated twice or more, as required.

Next, a thermoplastic resin layer 28 is formed on an insulatingsubstrate 2, thereby obtaining an object onto which the conductorpattern is transferred. The thermoplastic resin layer 28 functions as anadhesive layer when the conductor pattern is transferred. Asschematically shown in FIG. 6, the intaglio plate 20 and the insulatingsubstrate 2 are laminated together so that the surface of the intaglioplate 20, on which the groove 21 and the pit 22 filled with the Ag pasteare formed as described above, and the thermoplastic resin layer 28 faceeach other (Step 270).

As described later, if the thermoplastic resin layer 28 is excessivelythick, a large amount of combustion gas of the thermoplastic resin layer28 itself is generated during burning, and therefore the conductorpattern is not formed in a good condition. An examination carried out bythe inventors confirmed that a preferable thickness of the thermoplasticresin layer 28 is 20 μm or less.

It is desirable that the temperature during the laminating step 270 isset in the range from a temperature lower than the glass-transitiontemperature of the used thermoplastic resin layer 28 by 30° C. to onehigher than that by 100° C. If the laminating temperature is higher thanthe upper limit described above, the Ag paste 24 does not transfer wellfrom the groove 21 and the pit 22 of the intaglio plate 20. This isbecause the thermoplastic resin layer 28 has too much fluidity at thetemperature above the upper limit, and therefore the thermoplastic resinlayer 28 is thinned by the pressure during lamination.

On the other hand, if the laminating temperature is lower than the lowerlimit described above, the Ag paste 24 will not transfer well from thegroove 21 and the pit 22 of the intaglio plate 20, either. This isbecause the thermoplastic resin layer 28 does not have sufficientfluidity at the temperature below the lower limit, and therefore the Agpaste 24 and the thermoplastic resin layer 28 are not sufficientlyattached to each other.

Furthermore, it is desirable that the pressure during the lamination isset in the range from 1 kg/cm² to the critical pressure at which theinsulating substrate 2 is cracked. If the pressure is lower than that ofthe lower limit described above, the intaglio plate 20 and theinsulating substrate 2 are not perfectly attached to each other andcontain bubbles therebetween in the case where the surface of theinsulating substrate 2 has undulation. This phenomenon causes aninsufficient transfer of the Ag paste 24 in some cases. So thelaminating step 270 is conducted under the following conditions inExample 1.

First, a solution of butylcarbitolacetate, in which polyvinylbutyralresin (hereinafter, abbreviated as PVB) is dissolved, is applied to thesurface of a square insulating substrate 2, 100 mm×100 mm, made ofalumina and then dried. With this process, a PVB layer 28 having athickness of 10 μm is formed on the entire surface of the insulatingsubstrate 2. Next, the insulating substrate 2, on which the PVB layer 28is formed, and the intaglio plate 20 filled with the Ag paste 24 arelaminated together under the conditions of a temperature of 100° C., apressure of 20 kg/cm² and a speed of 5 cm/second, using thermal rollers26 and 27 as shown in FIG. 6. The PVB layer 28 may be applied by thedipping method, spinner method, or coating method using roll coaster.Although the PVB layer 28 is formed on only one surface of theinsulating substrate 2 in Example 1, the PVB layer 28 may be formed onboth the surfaces of the insulating substrate 2.

In general, the surface of the insulating substrate 2 has an undulationwith a maximum width of about 30 μm as diagrammatically shown in FIGS.7A and 7B. In the case where an intaglio plate 29 made of glass is usedas in the conventional process, the glass intaglio plate 29 has toostrong a rigidity to sufficiently follow the undulation shape of theinsulating substrate 2 as shown in FIG. 7B. For this reason, theintaglio plate 29 and the insulating substrate 2 should be laminated byusing an uneven PVB layer 28′ having a thickness in the range of 10 to50 μm so as to absorb the undulation. For this reason, it is impossibleto form the PVB layer 28′ having the thickness in the preferred range(20 μm or less) described above.

However, according to the structure of the present invention using theintaglio plate 20 made of resin having good flexibility, as shown inFIG. 7A, the intaglio plate 20 can sufficiently follow the undulation ofthe insulating substrate 2. Therefore, it is possible to form the PVBlayer 28 having a thickness of 10 μm or less on the insulating substrate2 regardless of the undulation of the insulating substrate 2.

Next, transfer step 280 is conducted. The temperature of the laminatedintaglio plate 20 and the insulating substrate 2 is lowered to roomtemperature, and then the intaglio plate 20 is peeled from theinsulating substrate 2, thereby transferring the patterned Ag paste 24.

Since the intaglio plate 20 has much greater flexibility, it is possibleto bend the intaglio plate 20 to 90° or more as shown in FIG. 8. As aresult, the peeling of the intaglio plate 20 from the insulatingsubstrate 2 is a peeling action of a line from the face. Therefore, itis possible to peel the intaglio plate 20 with ease since the requiredpeeling force is lowered.

On the other hand, in the case where the conventional glass intaglioplate 29 having strong rigidity (see FIG. 7B) is used, a large peelingforce is required since it is impossible to bend the intaglio 29 to theangle shown in FIG. 8 and therefore it becomes a peeling action of aface from a face. Moreover, if the conventional intaglio plate 29 isexcessively bent, cracking easily occurs in the intaglio plate 29 or theinsulating substrate 2. Therefore, much attention needs to be paid tothe peeling of the intaglio plate 29 from the insulating substrate 2.Thus, operational efficiency is low, and as a result, operational costsand operation time is increased.

According to the present invention, even if the intaglio plate 20, forexample, having a fine pattern including a groove with a width of 15 μmand a depth of 20 μm is used, the Ag paste 24 does not remain in thegroove 21. Thus, the conductor pattern having substantially the samewidth as that of the groove 21 and a height substantially the same asthe depth of the groove 21 can be transferred and formed. As for the viahole electrode, in the case where the pit 22 of the intaglio plate 20has a diameter of 45 μm and a depth of 60 μm, the conductor patternhaving the dimensions substantially perfectly corresponding to the pit22 can be transferred and formed. In addition, the conductive lines andthe via hole electrodes are formed simultaneously and integrally in thesame step, and thus electrical connection therebetween is surelyattained.

Furthermore, for electronic parts used in a high-frequency region suchas the chip inductor 1, it is necessary to make the surface shape of theconductor pattern as sharp as possible in order to improve electricoperating characteristics by lowering the skin resistance. However,since wet etching employed for forming a conventional copper plate and aglass intaglio plate is isotropic etching, it is impossible to processthe intaglio plate 20 with a high aspect ratio. Thus, it becomes moredifficult to form a deep groove as the pattern becomes finer andtherefore the width of a line to be formed becomes thinner. Moreover,edge portions of the groove are not sharply formed but rounded. On theother hand, if the intaglio plate 20 is processed by the excimer laseras in the present invention, it is possible to form the pattern havingacute edges. Furthermore, as described above, since the Ag paste 24 doesnot remain in the groove 21 and the pit 22 during the transfer of thepattern, the pattern having the sharp shape similar to that of the acuteintaglio plate 20 is transferred. Therefore, the conductor patternformed according to the present example has excellent characteristics asa conductor for high-frequency.

Next, Step 290 for burning the insulating substrate 2, onto which theconductor pattern has been transferred as described above, is carriedout under the temperature pattern with the peak temperature of 850° C.shown in FIG. 9. Since the insulating substrate 2 which is to be burntin the present invention has the structure in which the conductorpattern is formed on the PVB layer (a resin layer) 28, combustion gasmay be generated from the PVB layer 28 (depending on the burningconditions), resulting in the peeling or deformation of the conductorpattern and causing defects thereof. In order to prevent suchdisadvantages, it is desirable to set the temperature increase rate from200° C. to 500° C. (corresponding to the temperatures at which thecombustion of the PVB layer 28 is started and completed, respectively)at 200° C./hour or less.

As already described in conjunction with the laminating Step 270, therelation between the thickness of the PVB layer 28 and the performanceof the formed conductor pattern in the case where the burning step 290is carried out under the conditions described above is shown in Table 1.

TABLE 1 Thickness of Pattern shape after Peeling of pattern after PVBfilm burning burning  10 μm ◯ ◯  20 μm ◯ ◯  30 μm X Δ  50 μm X X 100 μmX X Criteria for evaluation In an alumina substrate of a size of 100 mm× 100 mm (2 × 1.25 mm in size 400 pieces) ◯ Desirable products: 95% ormore Δ Desirable products: 70% or more X Desirable products: 70% or less

It is understood from Table 1 that when the thickness of the PVB layer28 is 20 μm or less, a desired conductor pattern can be burnt withoutcausing deterioration in shape and the peeling. However, if thethickness of the PVB layer 28 is 30 μm or more, the shape of the patternis insufficiently formed and the undesirable peeling of the pattern isfound. Therefore it is characteristically advantageous for the PVB layer28 to have a small thickness. By the comparison between the polyimideintaglio plate 20 of the present invention and the conventional glassintaglio plate 29, referring to FIGS. 7A and 7B, it is understood thatthe conductor pattern of a higher quality is formed by using thepolyimide intaglio plate 20 of the present invention, since thethickness of the PVB layer 28 remains within a preferable range.

According to the method of the present invention, it is possible tointegrally and simultaneously form the line 3 in the conductor patternand the via hole electrode 7. Thus, reliable electrical connectionbetween line 3 and the via hole electrode 7 can be obtained.

Next, in order to form the insulating layer 5, a glass paste pattern isprinted on the surface of the insulating substrate 2 on which theconductor pattern made of Ag paste 24 is formed in the above steps (Step300). In this step, a portion corresponding to the via hole electrode 7is printed by a crystallized glass with a viscosity of 200 thousands cpsusing a screen plate with a mask diameter of 150 μm. As a result,bleeding of the print occurs around the via hole electrode 7 andtherefore the thickness of the glass paste covering the periphery of thevia hole electrode 7 becomes thinner than that in the other portion,thereby forming the via hole shape in the periphery of the via holeelectrode 7.

Since the diameter of the via hole to be formed is defined by the shapeof the via hole electrode 7, even a fine via hole, for example, having adiameter of about 40 μm which is conventionally difficult to form, canbe easily printed and formed according to the present invention.Moreover, since such fine via holes can be formed, the number of turnsof the spiral coil pattern can be increased, whereby an obtainedinductance value can be increased.

The glass paste pattern printed as described above is burnt by keepingit at a peak temperature of 820° C. for 10 minutes so as to form theinsulating layer 5. The crystallized glass used hardly flows duringburning and the printed pattern shape can be kept in good condition.

In a conventional method, the via hole for connecting the conductorpatterns of the upper and lower layers of the multilayered substrate toeach other is formed in such a manner that an opening in the insulatinglayer is provided by patterning in screen printing or etching and thenburying the via hole electrodes therein. In this method, however, if thevia hole electrode is insufficiently buried, the upper and/or lowerlayer conductor patterns are not sufficiently electrically connected tothe via hole electrode, thereby causing insufficient connection betweenthe conductor patterns of the upper and lower layers in some cases.However, as described above, in the method according to the presentinvention, since the via hole electrode 7 is integrally andsimultaneously formed with the conductor pattern of the lower layer,insufficient connection as described above does not occur.

Moreover, since the shape and thickness of the via hole electrode 7 canbe optionally set, it is possible to surely connect the upper conductorpattern to the via hole electrode 7 by forming the via hole electrode 7so as to protrude from the surface of the insulating layer 5 by severalμm. Moreover, by forming the via hole electrode 7 to have a trapezoidalsectional shape in a plane perpendicular to the surface of the substrate2, it is possible to obtain sufficient connecting strength required inthe succeeding steps even when the fine via hole electrode 7 is formed.

Lastly, Step 310 for forming a lead electrode 6 on the insulating layer5 is carried out. The pattern of the lead electrode 6 is printed on thesurface of the insulating layer 5 by screen printing using the Ag pasteand then burnt at a peak temperature of 810° C. for 10 minutes, therebyforming the lead electrode 6. With the formation of the lead electrode6, the chip inductor 1 of Example 1 is fabricated.

In the above description, the method for fabricating the electronicparts according to Example 1 is described, taking the chip inductor 1 asan example. However, it goes without saying that the electronic part tobe fabricated in accordance with the present invention is not limited tothe chip inductor 1. Other electronic parts can be formed such as a chipbead, an EMI filter, a condenser and the like, and any electrode portionof the electronic parts having a multilayered structure.

In the above description, after the conductor pattern is transferred andformed in Steps 210 to 290, the insulating layer 5 and the leadelectrode 6 are formed in Steps 300 and 310. Alternatively, in the casewhere a conductor pattern which does not require such a structure isformed, a desired conductor pattern can be obtained through Steps 210 to290 and Steps 300 and 310 do not have to be carried out.

Although the Ag paste is used as the material of the conductor pasteused for forming the conductor pattern, the material for the conductorpaste is not limited thereto. For example, other metal pastes such asCu, Ni, Al, and Au pastes, or resinate paste can be used. Alternatively,in place of the conductive paste containing the organic solvent, theconductive paste containing a UV-curable resin or a thermosetting resinhaving an appropriate flexibility after being cured may also be used.

As a material of the intaglio plate 20, besides the polyimide film 15described above, a resin sheet of, for example, PET, PSF, PC, PEI(polyetherimide), PAR (polyacrylate), or PEEK (polyetheretherketone) maybe used as long as they have an appropriate flexibility. As a materialof the resin layer 28 formed on the insulating substrate 2, an ethylcellulose type thermoplastic resin, or an epoxy or acrylic typethermosetting resin may be used.

Furthermore, in the laminating step of the intaglio plate 20 and theinsulating substrate 2 in the above description, the apparatus forthermally laminating while applying pressure using the thermal rollers26 and 27 is used. However, a pressing apparatus having a heating plateon at least one side may be used instead.

The material of the insulating substrate 2 constituting the object fortransferring and forming the conductor pattern thereon is not limited tospecific materials, and materials generally used such as ceramic can beused. Alternatively, a dielectric material including barium titanate asa main material may also be used.

Especially in the case where the inductance parts are formed, it isdesirable that at least one of the insulating substrate 2 and theinsulating layer 5 is formed of a magnetic material such as ferrite.This is because a magnetic permeability increases the resultantinductance value of the electronic parts to be formed.

Alternatively, the object can be formed of a green sheet. Since thegreen sheet has such a property that it is softened by heating, theformation of the resin layer 28, functioning as an adhesive layer whenthe conductor pattern is transferred in Step 270, can be omitted in thecase where the object is formed using the green sheet.

The excimer laser apparatus 11 is used for forming the intaglio plate20. However, other laser sources such as a dye laser or a free electronlaser can be used as long as they are capable of emitting a laser beamhaving a wavelength of the UV region. Furthermore, other light sourcescan also be used as long as they are capable of emitting a beam with anenergy density having a similar level to that of the above lasers in theabove wavelength region.

EXAMPLE 2

A second example of the present invention is described, taking a hybridIC (hereinafter, abbreviated as HIC) substrate as an example, withreference to FIGS. 11 to 14. In these figures, like components areindicated by the same reference numerals.

FIG. 11A shows a plan view of an HIC substrate 30, and FIG. 11B is across-sectional view of the HIC substrate 30 taking along a line11B-11B′ of FIG. 11A. The right part of FIG. 11A shows the portion wherethe conductor pattern of the upper layer is formed, and the left partshows the portion where the conductor pattern of the lower layer isformed. Since FIGS. 11A and 11B schematically show the structure of theHIC substrate 30, the conductor patterns in the figures do not preciselyreflect the values of the size described below.

The HIC substrate 30 has a double-layered wiring structure including alower layer conductor pattern 32 formed on an insulating substrate 31,an insulating layer 33 formed so as to cover the lower layer conductorpattern 32, and an upper layer conductor pattern 34 formed on theinsulating layer 33. As can be seen from FIG. 11B, the lower layerconductor pattern 32 includes a spiral coil conductor portion 32 a andthe other conductor potion 32 b. The lower layer conductor pattern 32and the upper layer conductor pattern 34 are connected to each otherthrough a via hole electrode 35. A mounting portion 36 for facedownmounting of an IC chip is provided on the portion of the upper layerconductor pattern 34. Facedown mounting of an IC chip is sometimesreferred to in the art as a “flip-chip mount.”

In view of the electrical characteristics, a conductor pattern, forexample, having a pitch of 60 μm (i.e., a width of each line is 30 μmand an interval between the lines is 30 μm) and a height (i.e., thethickness of a conductor film) of 35 μm, is formed in the portion of thelower layer conductor pattern 32 corresponding to the coil conductorportion 32 a. The via hole electrode 35 is formed so as to have a height(i.e., a thickness of the conductor film) of 50 μm so that the tip ofthe via hole electrode 35 protrudes from the surface of the insulatinglayer 33, thereby surely connecting the conductor patterns of the upperand lower layers 32 and 34. On the other hand, the facedown mountingportion 36 of the upper layer conductor pattern 34 is formed with, forexample, a pitch of 150 μm (i.e., a width of each line is 75 μm and aninterval between the lines is 75 μm).

Furthermore, the facedown mounting portion 36 is required to have such aflatness that the undulation for 5 mm of the surface in length is 3 μmor less from restriction in the facedown mounting conditions of the ICchip. In this case, when the height (the thickness of the conductorfilm) of the conductor pattern 32 b positioned below the facedownmounting portion 36 is 5 μm or more, the undulation of the surface ofthe insulating layer 33 becomes larger, thereby making it difficult toperform the facedown mounting. Therefore, the height of the conductorportion 32 b is restrained so as not to exceed 5 μm.

As described above, in Example 2 of the present invention, the conductorpattern having a difference in level is formed by altering the thicknessof the conductor film (the height of the line) at arbitrary positions inthe conductor pattern to be at a desired level. With this process, theHIC substrate 30 enabling the facedown mounting of the IC chip at apredetermined position of the uppermost surface of the upper layerconductor pattern 34 is formed.

Hereinafter, a method for fabricating the HIC substrate 30 of thepresent example will be described. Each step such as the forming step ofthe intaglio plate in the following description is substantiallyequivalent to each corresponding step of Example 1, except that theshape of the conductor pattern to be formed is different. Therefore, thedetailed description on its properties and the like is omitted.

First, an intaglio plate for forming the lower layer conductor pattern32 is formed on a polyimide film in the following order by employing theexcimer laser, using three types of masks, i.e., a mask for forming thecoil conductor portion 32 a, a mask for forming the other conductorportion 32 b of the lower layer conductor pattern 32, and a mask forforming the via hole electrode 35. First, a pattern which consists of agroove of 45 μm in depth corresponding to the coil conductor portion 32a is formed using the mask corresponding to the pattern of the coilconductor portion 32 a. Next, a pattern which consists of a groove of 65μm in depth corresponding to the via hole electrode 35 is formed usingthe mask corresponding to the pattern of the via hole electrode 35.Lastly, a pattern which consists of a groove of 10 μm in depthcorresponding to the conductor portion 32 b is formed using the maskcorresponding to the pattern of the conductor portion 32 b. The relativeposition of each pattern is aligned to an accuracy within 5 μm, therebyforming the intaglio plate for forming the lower layer conductor pattern32.

On the thus formed intaglio plate, a release layer made of afluorine-carbon monomolecular film is formed as in Step 220 ofExample 1. Next, as in Step 230 of Example 1, each groove of theintaglio plate is filled with the Ag paste using the squeegee made ofceramics. Thereafter, as in Step 240, the Ag paste is dried by thecirculating type hot air dryer so as to evaporate the organic solventincluded therein, thereby reducing the volume of Ag paste filling thegroove of the intaglio plate by the amount corresponding to theevaporated organic solvent. Furthermore, as in Steps 250 and 260, afterthe groove is refilled with the Ag paste, the Ag paste is dried in twostages. By repeating the steps of filling the groove with the Ag pasteand drying the Ag paste as in Example 1, the thickness of the film of Agpaste can be substantially the same as the depth of each groove.

Next, as in Step 270, the thermoplastic resin layer having a thicknessof 10 μm is formed on the surface of the insulating substrate 31. Then,the intaglio plate and the insulating substrate 31 are laminatedtogether at a pressure of 25 kg/cm² and a temperature of the substrateof 130° C. Thereafter, the temperature of the substrate is lowered toroom temperature and the intaglio plate is peeled from the insulatingsubstrate 31, thereby transferring the conductor pattern onto theinsulating substrate 31. Furthermore, as in Step 290, the insulatingsubstrate 31, on which the conductor pattern has been transferred issubjected to the burning treatment by raising temperature to a peakvalue of 850° C. with a temperature increase rate of 200° C./hour.

With the series of steps described above, it is possible tosimultaneously and integrally form the lower layer conductor pattern 32and the via hole electrode 35, as in Example 1.

Next, as in Step 300, a pattern of an insulating layer 33 is formed onthe insulating substrate 31 by screen printing of a glass paste. Then,the insulating substrate 31 is burnt at a temperature of 840° C.,thereby forming the insulating layer 33. By using the crystallized glassas in Example 1, the glass paste hardly flows during burning. Therefore,the shape formed by screen printing is kept in relatively goodcondition.

Next, a pattern corresponding to the upper layer conductor pattern 34 isformed by the screen printing of Ag paste, and then burnt by being keptat a peak temperature of 810° C. for 10 minutes so as to form the upperlayer conductor pattern 34.

As in the above steps, a coil having excellent electricalcharacteristics as in Example 1 is formed by increasing the height ofthe line (the thickness of the conductor film) at the portioncorresponding to the spiral coil conductor 32 a. The via hole electrode35 is formed so as to have a trapezoidal cross-section in a planeperpendicular to the surface of the substrate, thereby surelyelectrically connecting the upper layer conductor pattern 34 to thelower layer conductor pattern 32. Moreover, the thickness of the lowerlayer conductor pattern 32 is selectively thinned at a predeterminedportion, thereby realizing desired flattening at a portion of thesurface of the insulating layer 33 required to be flattened. With theseprocesses, the HIC substrate 30, on which the IC chip can be mounted byfacedown mounting, is fabricated.

The shape of the via hole electrode 35 is not limited to the one shownin FIG. 11B. For example, as in the HIC substrate 40 shown in FIG. 12,it is possible to form an electrode 35′ of the shape partly burying thevia hole. Alternatively, the insulating layer 33 may be formed so as notto entirely cover the lower layer conductor pattern 32 by providing thevia hole during the insulating layer formation. Then an electrodeconnecting the upper and lower layer conductor patterns 32 and 34 may beformed within the via hole as the subsequent step.

Furthermore, in the above description, the present invention isdescribed by taking the double-layered wiring substrate as an example.However, it is possible for the substrate to have a further multilayeredstructure. In the HIC substrate 50 shown in FIG. 13, conductor patterns51, 52, and 53 respectively corresponding to the pattern of a singlelayer of the HIC substrates 30 or 40 shown in FIG. 11B or 12 aredeposited so as to form a multilayered structure including three layers.

Moreover, according to the present invention, it is possible to formlines in the conductor pattern so as to have a difference in level.Therefore, an HIC substrate 60 including an insulating layer 33 with asurface form as shown in FIG. 14 can be formed. In the HIC substrate 60,the conductor portion 32 a of the lower layer conductor patterncorresponding to the portion in which the surface undulation of theinsulating layer 33 is not required to be controlled is formed as arelatively high line (a thick conductor film). On the other hand, theconductor portion 32 b corresponding to the portion in which the surfaceof the insulating layer 33 is required to be flattened, such as thefacedown mounting portion for an IC chip 61, is formed with a relativelylow line (a thin conductor film). Conductor resistance increases as theheight of the conductor portion 32 b becomes lower. However, it ispossible to restrain the disadvantageous effects on the electricalcharacteristics by setting the width of the lines of the conductorportion 32 b at a large value as required.

As described above, according to the present invention, it is possibleto obtain the most suitable form of the conductor pattern inconsideration of the trade-off between the design requirement for theform of the surface of the insulating layer 33 and the requirement forthe electrical characteristics of the conductor pattern.

As described above, according to the method for fabricating electronicparts of the present invention, a groove pattern corresponding to theyet to be formed conductor pattern is formed by an excimer laser on asurface of a resin sheet with a high flexibility, whereby an intaglioplate is formed. A conductive paste filling the groove pattern issubstantially perfectly transferred on the substrate which is an object.Since it is possible to make the groove on the intaglio plate verysharp, the conductor pattern formed through burning after transfer alsohas a desired acute rectangular shape. With this shape, the electricalcharacteristics of the conductor pattern to be formed are improved.

As for the size, it is possible to form such a fine and thick conductorpattern that the width of lines in the conductor pattern is 10 μm orless and the thickness of the conductor film is 5 μm or more. Moreover,it is possible to thickly form the conductor film only for an optionalpredetermined portion, that is, to set the lines of the conductorpattern high. By applying these aspects, according to a method forfabricating electronic parts of the present invention, it is possible toform a via hole with a fine width substantially equivalent to the sizeof the fine conductor pattern. Therefore, a small electronic part havinga multilayered structure, which was difficult to realize in conventionalprinting methods, can now be fabricated at low cost.

The present invention has been described above by taking a type ofelectronic part which requires the formation of the thick conductor filmin the conductor pattern as an example. However, it is apparent to thoseskilled in the art that the method for fabricating electronic parts ofthe present invention is applicable to other electronic parts as well,i.e., especially, electronic parts which do not require to have adifference in thickness of the conductor film or the thick portiontherein. Even in such a case, advantageous aspects of the invention,such as easily and surely peeling the intaglio plate from the insulatingsubstrate in the transfer step by using the intaglio plate made of theflexible resin sheet and making the intaglio pattern acute andrectangular by forming the intaglio pattern with an excimer laser, makeit possible to improve the characteristics of the electronic parts to beformed.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. An electronic part made in accordance with amethod comprising the steps of: transferring a first continuousconductor pattern onto a thermoplastic resin layer formed on a surfaceof a substrate by intaglio printing using an intaglio plate having acured conductive paste therein which provides the first continuousconductor pattern, wherein the intaglio plate is a laser processed resinsheet having high flexibility and the cured conductive paste includes aplasticizer; forming an insulating layer which covers at least a portionof the first continuous conductor pattern and which forms an uncoveredportion of the first continuous conductor pattern; and forming a secondconductor pattern on a surface of the insulating layer, wherein theintaglio plate formed with the resin sheet of high flexibility providesa means for transferring the first continuous conductor pattern onto thethermoplastic resin layer formed on the surface of the substrate, wherethe thermoplastic resin layer and the surface of the substrate areundulating substrate surfaces, the first continuous conductor patternhas a trapezoidal cross-sectional shape, a bottom portion of the firstcontinuous pattern adjacent the surface of the substrate being widerthan a top portion of the first continuous conductor pattern, and thefirst continuous conductor pattern has a width adjacent the substrate ofabout 50 μm or less, and has a thickness of about 5 μm or more, and thefirst continuous conductor pattern includes the plasticizer of the curedconductive paste.
 2. An electronic part according to claim 1, the methodfurther comprising the step of forming an electrode at the uncoveredportion of the first continuous conductor pattern for electricallyconnecting the first continuous conductor pattern and the secondconductor pattern.
 3. An electronic part according to claim 1, wherein adifference in height is provided between portions of the firstcontinuous conductor pattern.
 4. An electronic part according to claim3, wherein a raised portion of the first continuous conductor pattern isused as an electrode for electrically connecting the first continuousconductor pattern and the second conductor pattern.
 5. An electronicpart according to claim 4, wherein the first continuous conductorpattern includes a reduced height portion, said reduced height portioncorresponding to a position on the surface of the insulating layer atwhich a flattened portion is provided.
 6. An electronic part accordingto claim 5, further comprising an IC chip flip-chip mounted onto theflattened portion on the surface of the insulating layer.
 7. Anelectronic part according to claim 1, wherein the first continuousconductor pattern has a side face with a tapered angle in the range ofabout 2° to about 60° with respect to a direction perpendicular to a topsurface of the first continuous conductor pattern.
 8. An electronic partaccording to claim 1, the method further comprising the step ofproviding an adhesive layer on the surface of the substrate so that thefirst continuous conductor pattern is transferred on a surface of theadhesive layer, the adhesive layer having a thickness of about 20 μm orless.
 9. An electronic part, comprising: a substrate; a thermoplasticresin layer formed on a surface of the substrate; a first continuousconductor pattern transferred onto the thermoplastic resin layer formedon the surface of the substrate by intaglio printing using an intaglioplate having a cured conductive paste therein which provides the firstcontinuous conductor pattern, wherein the intaglio plate is a laserprocessed resin sheet having high flexibility and the cured conductivepaste includes a plasticizer, a difference in height being providedbetween portions of the first continuous conductor pattern; aninsulating layer which covers at least a portion of the first continuousconductor pattern; and a second conductor pattern formed on a surface ofthe insulating layer, wherein the intaglio plate formed with the resinsheet of high flexibility provides a means for transferring the firstcontinuous conductor pattern onto the thermoplastic resin layer formedon the surface of the substrate, where the thermoplastic resin layer andthe surface of the substrate are undulating substrate surfaces, a raisedportion of the first continuous conductor pattern is used as anelectrode for electrically connecting the first continuous conductorpattern and the second conductor pattern, and the first continuousconductor pattern includes a reduced height portion, said reduced heightportion corresponding to a position on the surface of the insulatinglayer at which a flattened portion is provided, further wherein thefirst continuous conductor pattern has a trapezoidal cross-sectionalshape, a bottom portion of the first continuous conductor patternadjacent the surface of the substrate being wider than a top portion ofthe first continuous conductor pattern, and the first continuousconductor pattern has a width adjacent the substrate of about 50 μm orless, and has a thickness of about 5 μm or more, and the firstcontinuous conductor pattern includes the plasticizer of the curedconductive paste.
 10. An electronic part according to claim 9, furthercomprising an IC chip facedown-mounted onto the flat portion on thesurface of the insulating layer.
 11. An electronic part made inaccordance with a method comprising the steps of: transferring a firstcontinuous conductor pattern onto a thermoplastic resin layer formed ona surface of a substrate made of a green sheet by intaglio printingusing an intaglio plate having a cured conductive paste therein whichprovides the first continuous conductor pattern, wherein the intaglioplate is a laser processed resin sheet having high flexibility and thecured conductive paste includes a plasticizer; forming an insulatinglayer which covers at least a portion of the first continuous conductorpattern and which forms an uncovered portion of the first continuousconductor pattern; and forming a second conductor pattern on a surfaceof the insulating layer, wherein the first intaglio plate formed withthe resin sheet of high flexibility provides a means for transferringthe first continuous conductor pattern onto the thermoplastic resinlayer formed on the surface of the substrate made of a green sheet,where the thermoplastic resin layer and the surface of the substratemade of a green sheet are undulating substrate surfaces, the firstcontinuous conductor pattern has a trapezoidal cross-sectional shape, abottom portion of the first continuous conductor pattern adjacent thesurface of the substrate being wider than a top portion of the firstcontinuous conductor pattern, and the first continuous conductor patternhas a width adjacent the substrate of about 50 μm or less, and has athickness of about 5 μm or more, and the first continuous conductorpattern includes the plasticizer of the cured conductive paste.
 12. Anelectronic part according to claim 11, the method further comprising thestep of forming an electrode at the uncovered portion of the firstcontinuous conductor pattern for electrically connecting the firstcontinuous conductor pattern and the second conductor pattern(s).
 13. Anelectronic part according to claim 1, wherein a difference in height isprovided between portions of the first continuous conductor pattern. 14.An electronic part according to claim 13, wherein a raised portion ofthe first continuous conductor pattern is used as an electrode forelectrically connecting the first continuous conductor pattern and thesecond pattern.
 15. An electronic part according to claim 14, whereinthe first continuous conductor pattern includes a reduced heightportion, said reduced height portion corresponding to a position on thesurface of the insulating layer at which a flattened portion isprovided.
 16. An electronic part according to claim 15, furthercomprising an IC chip flip-chip mounted onto the flattened portion onthe surface of the insulating layer.
 17. An electronic part according toclaim 11, wherein the first conductor pattern has a side face with atapered angle in the range of about 20° to about 60° with respect to adirection perpendicular to a top surface of the first continuousconductor pattern.
 18. An electronic part, comprising: a substrate; athermoplastic resin layer formed on a surface of the substrate; a firstcontinuous conductor pattern transferred onto the thermoplastic resinlayer formed on the surface of the substrate by intaglio printing usingan intaglio plate having a cured conductive paste therein which providesthe first continuous conductor pattern, wherein the intaglio plate is alaser processed resin sheet having high flexibility and the curedconductive paste includes a plasticizer, a first conductor portion ofthe first continuous conductor pattern having a height which is higherthan the height of a second conductor portion thereof; an insulatinglayer which covers at least a portion of the first continuous conductorpattern; and a second conductor pattern formed on a surface of theinsulating layer, wherein the intaglio plate formed with the resin sheetof high flexibility provides a means for transferring the firstcontinuous conductor pattern onto the thermoplastic resin layer formedon the surface of the substrate, where the thermoplastic resin layer andthe surface of the substrate are undulating substrate surfaces, thefirst continuous conductor pattern is substantially limited to conductorportions with trapezoidal cross-sectional shapes, the first continuousconductor portion serving as an electrode connecting the firstcontinuous conductor pattern to the second conductor pattern through theinsulating layer, and the first continuous conductor pattern has a widthadjacent the substrate of about 50 μm or less, and has a thickness ofabout 5 μm or more, and the first continuous conductor pattern includesthe plasticizer of the cured conductive paste.
 19. An electronic partcomprising: a substrate having an undulating surface; a thermoplasticresin layer formed on a surface of the substrate also having anundulating surface; a first continuous conductor pattern beingtransferred onto the thermoplastic resin layer formed on the surface ofthe substrate by intaglio printing using an intaglio plate having acured conductive paste therein which provides the first continuousconductor pattern, wherein the intaglio plate is a laser processed resinsheet having high flexibility and the cured conductive paste includes aplasticizer, and wherein the first continuous conductor pattern has atrapezoidal cross-sectional shape, a bottom portion of the firstcontinuous pattern adjacent the surface of the substrate being widerthan a top portion of the first continuous conductor pattern, and thefirst continuous conductor pattern has a width adjacent the substrate ofabout 50 μm or less, and has a thickness of about 5 μm or more; aninsulating layer covering at least a portion of the first continuousconductor pattern and forming an uncovered portion of the firstcontinuous conductor pattern; and a second conductor pattern beingformed on a surface of the insulating layer, wherein the firstcontinuous conductor pattern includes the plasticizer of the curedconductive paste.
 20. An electronic part comprising: a substrate havingan undulating surface, wherein the substrate comprises a green sheet; athermoplastic resin layer formed on a surface of the substrate alsohaving an undulating surface; a first continuous conductor pattern beingtransferred onto the thermoplastic resin layer formed on the surface ofthe substrate by intaglio printing using an intaglio plate having acured conductive paste therein which provides the first continuousconductor pattern, wherein the intaglio plate is a laser processed resinsheet having high flexibility and the cured conductive paste includes aplasticizer, and wherein the first continuous conductor pattern has atrapezoidal cross-sectional shape, a bottom portion of the firstcontinuous pattern adjacent the surface of the substrate being widerthan a top portion of the first continuous conductor pattern, and thefirst continuous conductor pattern has a width adjacent the substrate ofabout 50 μm or less, and has a thickness of about 5 μm or more; aninsulating layer covering at least a portion of the first continuousconductor pattern and forming an uncovered portion of the firstcontinuous conductor pattern; and a second conductor pattern beingformed on a surface of the insulating layer, wherein the firstcontinuous conductor pattern includes the plasticizer of the curedconductive paste.